For Mohamed Fayed, doting father of Diana’s boyfriend Dodi, is still convinced the pair were just hours from announcing wedding plans — and that they were killed by security services, on the orders of Prince Philip, to prevent the Princess marrying a Muslim.

His outrageous claim made the then Harrods owner a pariah in many circles. In 2000 the store was stripped of its four royal warrants — the right to declare that a company supplies goods by appointment to the Royal Family.

The tycoon then funded a £2million documentary which erroneously alleged that the Duke of Edinburgh had a Nazi background.

In the film — never aired for legal reasons — he set fire to the royal warrant emblems which had hung outside the department store.

In the 1990s Egyptian-born Fayed twice applied for British citizenship but was turned down by the Government. The first time he was rejected in 1994 led him to claim he had paid MPs to ask parliamentary questions on his behalf.

The episode became known as the “cash for questions” affair and led to the end of several Tory MPs’ careers.

French emergency workers in the tunnel where the fatal accident happened

“In a way, the Princess was having her youth again because she had been in the Royal Family for 15 years.

“This was her first affair as a free woman. She didn’t hide the relationship or sneak away. She’d been divorced since the year before.

“She had been either married or separated during every other affair she’d had, with men like James Hewitt and James Gilbey.

“People say it was just a summer fling with Dodi but they had been friends for ten years.

“In 1987, when William was five and Harry three, she was out shopping in the West End and went into Turnbull & Asser, the posh shirt maker in Jermyn Street, to get shirts for Charles and pyjamas for her sons.

“There she met Dodi. They got on well and saw each other again at film premieres or around town, but there was never an affair.

New Diana information assessed by Scotland Yard

“Then in 1997 they met in the South of France when Dodi was over there with friends and she was on holiday with William and Harry.

“They arranged to meet in London and at some point later friendship turned into something deeper.” The tragedy happened in the early hours of Sunday, August 31, 1997, when the limo in which Diana and Dodi were travelling hit a pillar at high speed in a Paris underpass.

Dodi, 42, and driver Henri Paul died instantly. Emergency services cut badly injured Diana from the wreckage but she was later pronounced dead in hospital.

The friend told us: “Mohamed remains confident that information will emerge confirming his belief that Dodi and Diana were deliberately killed by the security services.

He always says, ‘My son was slaughtered’, and he believes that was because the Establishment would not allow a Muslim to be married to the woman who would be the mother of the future king.”

This week, as he has done every summer for decades, Fayed has been holidaying near St Tropez, on the French Riviera, where he mostly sits in quiet solitude on his yacht Sakara.

This month the tycoon — who sold Harrods to a Qatari enterprise for £1.5billion in 2010 — will return home to Surrey to be near his dead son.

In 1997, while the nation marked Diana’s death with a State funeral at Westminster Abbey that was broadcast globally, millionaire film producer Dodi had a simple Muslim ceremony at Regent’s Park Mosque.

His body was buried in an ordinary plot at Brookwood Cemetery near Woking, Surrey.

The headstone read simply “Dodi”. Only the round-the-clock watch by security guards marked it out as the grave of the man who died beside the most famous woman in the world. After the Muslim tradition of 40 days of mourning, Dodi’s body was exhumed by night and moved 25 miles to the Fayed estate, where he was reburied in another simple grave.

Meanwhile, workmen built an elaborate burial chamber where one day Fayed will also be laid to rest next to his first-born son.

Jury concluded that Diana and Dodi were unlawfully killed by the gross negligence of both their chauffeur, Henri Paul and the paparazzi

For now, Fayed lives out his twilight years still believing in his conspiracy theory about Dodi and Diana. But the evidence shows they died when Henri Paul, who had alcohol in his blood, drove at high speed to outrun paparazzi photographers.

An inquest jury found no evidence that the crash was a Government plot. Instead it decided the couple had been unlawfully killed by a combination of Paul’s driving and the behaviour of vehicles behind them.

Fayed’s friend says: “Has he got any conclusive evidence of murder?

“No. But he hopes that he will live long enough to see proof of what he has always believed.”